1. Field of the Invention
The present invention relates to a process for the catalytic hydrogenation of nitrobenzene to aniline in the gas phase using a palladium-containing supported catalyst.
2. Discussion of Prior Art
Palladium-containing supported catalysts for carryout catalytic hydrogenation reactions, inter alia also of nitro-aromatic compounds, are generally known. The supports used industrially as the starting base material for the corresponding supported catalysts have, however, considerable disadvantages. Thus, because of the nature of their surface, the support materials are not inert and therefore as a rule cause undesired by-products to be formed. Furthermore, the application of the palladium to these supports in general results in a uniform distribution of the Pd over the entire grain of the support. This results in unnecessarily high catalyst costs, since, as is known, the active substances deposited inside the grain of the support either take no part in the reaction to be catalyzed or participate in this reaction to only a minor extent. For example, aluminum spinels, especially alkali metal or alkaline earth metal spinels, are employed as support materials for palladium catalysts for the reduction of nitroaromatic compounds. When such alkali metal aluminum spinels or alkaline earth metal aluminum spinels are prepared, varying residual amounts of water-soluble alkali metal or alkaline earth metal remain dispersed in the grain of the support, due to the process. Due to this inhomogeneity of the spinel, inhomogeneous deposition of the active substances in the individual grains of the support necessarily results. As a consequence of this, undesired differences in activity, selectivity and life arise when these aluminum spinel catalysts are employed industrially German (BRD) Offenlegungesschrift 2,135,155.
Since the catalytic hydrogenation of nitrobenzene to aniline is a large-scale industrial process an aniline is required in large amounts as an important intermediate product in the preparation of pharmaceuticals and dyestuffs and duct in the preparation of pharmaceuticals and dyestuffs and of monomers for polymerization, there continues to be a growing interest in improving this process by eliminating the above mentioned disadvantages.